1. Field of the Invention
This document relates to a stereoscopic image display device and driving method thereof capable of implementing a two-dimensional plane image (referred to as a ‘2D image’, hereinafter) and a three-dimensional stereoscopic image (referred to as a ‘3D image’).
2. Discussion of Related Art
A 3D image display device displays a 3D image by using a stereoscopic technique or an autostereoscopic technique.
The stereoscopic technique, which uses a parallax image of user's left and right eyes having a high stereoscopic effect, includes a glass method and a non-glass method which have been put to practical use. In the glass method, a left and right parallax image is displayed on a direct view-based display device by changing a polarization direction of the left and right parallax image or according to a time-division scheme, and a stereoscopic image is implemented by using polarization glasses or liquid crystal shutter glasses. In the non-glass method, generally, an optical plate such as a parallax barrier or the like for separating an optical axis of the left and right parallax image is installed in front of or behind a display screen.
A stereoscopic image display device employing a glass method as shown in FIG. 1 implements a stereoscopic image by using polarization characteristics of a patterned retarder 5 disposed on a display panel 3 and polarization characteristics of polarization glasses 6 worn by a user. The stereoscopic image display device alternately displays a left-eye image (L) and a right-eye image (R) on the display panel 3 and converts the characteristics of polarized light made incident to the polarization glasses 6 through the patterned retarder 5. The stereoscopic image display device may spatially divide the left-eye image (L) and the right-eye image (R) viewed by the user by differentiating the characteristics of polarized light of the left-eye image (L) and the characteristics of polarized light of the right-eye image (R) in order to implement a 3D image. In FIG. 1, reference numeral 1 denotes a backlight unit irradiating light to the display panel 3, and reference numerals 2 and 4 denote polarizer films attached to upper and lower plates of the display panel 3 in order to select a linear polarized light, respectively.
The stereoscopic image display device illustrated in FIG. 1 has a degraded visibility of a 3D image due to crosstalk generated at the position of a vertical viewing angle. Actually, only light of the left-eye image is supposed to pass through user's left eye and only light of the right-eye image is supposed to pass through user's right eye, and in this case, if light of left-eye image and light of the right-eye image are all made incident to user's left and right eyes, the user is bound to feel crosstalk. When the user views the display panel 3 from an upper side or from a lower side, not from a front side, light of the left-eye image and light of the right-eye image pass through a left-eye patterned retarder and a right-eye patterned retarder, respectively, at a vertical viewing angle greater by more than a certain angle than a front viewing angle, generating crosstalk. Thus, the stereoscopic image display device has a very narrow viewing angle at which a 3D image can be viewed without crosstalk.
Japanese Laid Open Publication No. 2002-185983 proposes a method for forming black stripes (BS) on a patterned retarder in order to increase the vertical viewing angle of the stereoscopic image display device as illustrated in FIG. 1. In this method, when the user observes the stereoscopic image display device at a location away by a certain distance (D) from the stereoscopic image display device, theoretically, a vertical viewing angle (α) at which no crosstalk is generated relies on the size of a black matrix (BM) formed on the display panel, the size of a black stripe (BS) formed on the patterned retarder, and the distance (S) between the display panel and patterned retarder. The vertical viewing angle (α) widens as the size of the black matrix (BM) and the black strip (BS) increases and as the distance (S) between the display panel and the patterned retarder decreases.
The stereoscopic image display device having the black stripes (BS) on the patterned retarder as shown in FIG. 2, however, has the following problems.
First, although the black stripes (BS) formed on the patterned retarder contribute to improve the vertical viewing angle of the stereoscopic image display device to a degree, they interact with the black matrixes (BM) formed on the display panel, causing moiré. Thus, when a 2D image is displayed on the stereoscopic image display device, visibility of the 2D image is drastically degraded due to moiré. FIG. 3 shows the results of an experimentation obtained by observing a 2D image displayed on a 47-inch stereoscopic image display device at a location 4-meter away from the stereoscopic image display device after black stripes are formed on a patterned retarder of the stereoscopic image display device. This experimentation results reveal that moirés of some 90 mm, 150 mm, and 355 mm are seen at observation locations A, B, and C, respectively.
Second, when a 2D image is displayed on the stereoscopic image display device, the luminance of the 2D image is significantly degraded due to the presence of the black stripes (BS) on the patterned retarder. This is because the black stripes (BS) formed on the patterned retarder cover some pixels of the display panel.